1. Field of the Invention
The invention relates to a process and a plant for the sterilization of sheet material utilized for packaging pre-sterilized products in aseptic conditions.
2. Description of the Prior Art
Using steam for sterilizing purposes is generally known in the art. U.S. Pat. No. 4,537,007 as early as in 1985 taught to spray superheated steam onto a sheet of packing material passed through a sterilizing chamber, with the sheet of packing material being, however, previously moved through a relatively hot water bath held at a temperature immediately below the boiling point, and at the same time hermetically sealing the bottom inlet port of the sterilizing chamber.
It appears that the process according to U.S. Pat. No. 4,537,007 could not be realized in practice. The reasons herefore, in all probability, reside in that it is difficult for the sheets of packing material usually consisting of plastic material suitable for packing purposes to be uniformly wetted with water and that the said process does not produce a coherent and uniform condensate film on the sheet of packing material. However, a hot condensate film is mandatory for achieving reliably sterile conditions. Since, in addition, the sheet of packing material according to the process of U.S. Pat. No. 4,537,007 is heated by the hot water bath itself, entering the sterilization chamber wetted with drops of water only, if wetted at all, the effect of the superheated steam which apparently is to serve especially for drying the sheet of packing material, is non-uniform because the steam is applied both to wetted and unwetted areas of the sheet material. Moreover, the steam is already fed to the sterilizing chamber in superheated condition requiring a superheating aggregate outside the chamber and correspondingly insulated steam feeding conduits; in addition, it will have to be taken into consideration that, as a rule, only saturated steam networks are available in the installation rooms of packing machines.
One object of the invention described herein is that of providing a sterilization process, and plant herefore, with the aid of which supplied saturated steam first is economically transformed therein into superheated steam where it is needed to be jetted in the form of superheated steam onto the non-pretreated sheet of packing material entering in dried condition to form thereon a uniformly thin film of condensate.
The above objects and others besides are realized by the process and plant to which the invention refers, being of a type utilizing an endless sheet of material for subsequent shaping into a strip and/or a tube having cups shaped thereinto by deep drawing, and being characterized in that the sterilization process itself comprises the following steps: Sterilization is effected by means of steam jetted through at least one nozzle, with the aseptic sheet of packing material being subsequently introduced into a sterile tube of a packing machine, and the sterilization chamber and the sterile tube being held at a slight excess pressure relative to the atmosphere. In accordance with the invention, saturated steam is supplied to the nozzle, and the saturated vapor prior to being applied to the section of the sheet of packing material contained in the sterilization chamber and supplied in dry condition into the chamber, by a controlled energy supply, immediately before jetting is superheated and the superheated vapor is jetted with substantially uniform intensity across the entire length of at least one transverse line of the sheet of packing material onto the same while forming a condensate film.
The process of the invention to be described hereinafter in greater detail can be realized both with a movement of she sheet of packing material relative to the nozzle and in standstill condition of the sheet of packing material.
A process slightly differing from the afore-described process comprises the following steps: Here, sterilization is again effected by steam jetted through at least one nozzle, with the sterilized sheet of packing material being subsequently introduced into a sterile tube of a packing machine, and with the sterilization chamber and the sterile tube being held under a slight excess pressure relative to the atmosphere. In accordance with the invention, saturated steam is supplied to the nozzle, and the saturated steam prior to being applied to the section of sheet of packing material contained in the sterilization chamber and introduced in timed sequence and in dry condition into the chamber immediately before being jetted is superheated by a controlled energy supply. The said superheated steam, within a steam stowage space formed above the section of the sheet of packing material to be treated and held in closed condition during steaming, is jetted onto the sheet of packing material throughout the entire surface thereof with substantially uniform intensity, forming at the same time a condensate film.
After sterilization, according to both processes the sterilized sheet of packing material in sterile condition, within a tube, is moved into the packing machine to be formed therein also under sterile conditions, into packings then filed and sealed.